1. Field of the Invention
This invention relates to foamed plastics, also known as cellular plastic or plastic foams. More particularly, it relates to foamed plastics coated with binder compositions to increase the flame and heat resistance properties of the plastic foams.
This invention especially relates to foamed plastics having formed thereon coatings of an inorganic binder composition, optionally utilized in combination with a dissimilar binder.
2. Description of the Prior Art
Ceramics and/or glass fibers have been used heretofore to prepare high temperature electrical insulating tape. U.S. Pat. No. 4,358,500 discloses refractory coated insulating compositions wherein the refractory coating, comprising refractory materials and an inorganic bonding agent, is formed on the surface and, necessarily, the interstices of a porous base fabric, such as a knitted fiberglass fabric. In the presence of extreme temperatures and heat, the refractory materials fuse into the softened surface of the base fabric, enabling it to withstand intense heat, flame impingement, flame abrasion and elevated temperatures well beyond the normal temperature limitations of the fabric. The resulting fabric structure will have ceramic qualities and will not soften, melt, drip or lose its insulating properties.
The inorganic bonding agent disclosed in U.S. Pat. No. 4,358,500 is prepared from colloidal silica, monoaluminum phosphate (MAP) and aluminum chlorohydrate (ACH) by adding the MAP and ACH separately to the colloidal silica which acts as a liquid moderator. Although the compositions containing the inorganic bonding agent of U.S. Pat. No. 4,358,500 may be exposed to high temperatures, no products of combustion in the form of smoke or fumes are produced as with other prior art coated fabrics. Further, the refractory coated compositions prepared with the inorganic bonding agent proved superior to inorganic coatings available for use on fabrics or paper substrates. The latter inorganic coatings could be damaged by water. They could be wet by water and the water could solvate the coating to the point of causing the inorganic coating to dissociate itself from the substrate. Although other binders, such as the acrylics, inhibited this wetting action, they would burn off when subjected to flame and high temperature. The refractory coated substrates disclosed in the '500 patent, on the other hand, are not wetted by water and are not subject to the solvation action of water as are other inorganic coatings. However, despite these advantages, the refractory coated compositions of the '500 patent exhibit a very undesirable feature. This refractory coating must be applied to a porous fabric so that the coating will be placed in the interstices of the fabric. This is necessary to achieve the formation of the refractory coating on this fabric. However, this requires the use of a larger quantity of the refractory coating when preparing these compositions to the extent that the coating in many instances constitutes about 50% of the overall weight of the impregnated base fabric. The result of all this is that when this coated fabric is flexed, the bond of the refractory coating to the substrate is disrupted and some particles may be released to the surface resulting in "dusting" of the coating. This, of course, is highly undesirable despite the very desirable features of flame and high temperature resistance which are exhibited by these refractory coated compositions.
U.S. application Ser. No. 598,864, application Ser. No. 688,693, and application Ser. No. 585,909 (now U.S. Pat. No. 4,507,355) relate to improvements in the inorganic bonding agent disclosed in the '500 patent by preparing an inorganic bonding agent from colloidal silica, monoaluminum phosphate, aluminum chlorohydrate and an organic tin halide catalyst. When this bonding agent is combined with refractory material and applied to base fabrics, it provides refractory-binder coated compositions which do not "dust" as those disclosed in the '500 patent. Briefly, this improved inorganic binder comprises the three components of the prior art bonding agent of the '500 patent to which is added a catalyst which promotes the curing of the binder when it is applied to an appropriate surface and increases the bond between this surface and the binder compositions.
A foamed plastic has been defined as a plastic, the apparent density of which is decreased substantially by the presence of numerous cells disposed throughout its mass. As used herein, the terms foamed plastic, cellular plastic or plastic foam are used interchangeably to denote two-phase gas-solid systems in which the solid is continuous and may be composed of a synthetic polymer. Foamed plastics can be classified generally as either rigid or flexible and within the rigid foams structural foams are rigid foams produced at greater than about 320 kg/m.sup.3 density.
Foamed plastics can be prepared by a variety of methods. The most important process consists of expanding a fluid polymer phase to a low density cellular state and then preserving this state. The foaming process consists usually of three steps: creating small discontinuities or cells in a fluid or plastic phase, causing these cells to grow to a desired volume and stabilizing this cellular structure by physical or chemical means. In the chemical stabilization, a fluid resin is polymerized into a three dimensional thermally set polymer, while in physical stabilization, an expanded thermoplastic polymer is cooled to a temperature below its second-order transition temperature or its crystalline melting point to prevent polymer flow.
The processes for preparing foamed plastics can be classified by techniques that are utilized in the cell growth and stabilization portions of the processes. Cell growth is initiated and controlled by lowering the external pressure or by increasing the internal pressure in the cells. Cell structure may be generated by dispersing gas in the fluid and then stabilizing this cellular state or by sintering polymer particles in a structure that contains a gas phase. Foamable compositions in which the pressure within the cells is increased have generally been called expandable formulations, while the cellular plastics produced by the decompression processes are catagorized by the methods employed in this process which includes extrusion, injection molding or compression molding. Among the polymers which may be utilized to prepare foamed plastics are polystyrene, poly(vinyl chloride), polyethylene, polyurethane, polyisocyanurate, polyphenols, epoxy resins, silicone resins, cellulose acetate, polyolefins, urea, formaldehyde resins, polyimide resins, polyamide resins, polyamide-imide resins and the like.
Examples of foamed plastics include foam polystyrene sheet used for meat and produce trays, egg cartons, snack food serving trays and disposable dinnerware. Foamed plastics also find use in their flexible form for comfort cushioning in automobile padding, seats, furniture, flooring, mattresses and pillows. Foam plastics also find use as thermal insulation, particularly in its rigid form. The low thermal conductivity of low density cellular polymers has been the main factor in their use as insulating materials for construction, pipe and vessel insulation and buoyancy devices in boats, floating docks and buoys. Rigid foamed plastics also find use as structural members in the construction industry.
When used as insulation in residential and commercial structures, in aircraft and ships, in electronic and electrical cabinets and for steam and fluid piping, these materials provide satisfactory low thermal conductivity properties. However, when subjected to high temperatures or flame abrasion, the foamed plastics may fail by melting and/or vaporizing to give off noxious and sometimes dangerous fumes. A means to improve the flame and heat resistance of such plastic foams would be extremely desirable and useful.
It is an object of this invention to provide plastic foams having improved heat and flame resistance.
It is another object of this invention to increase the heat and flame resistance of foamed plastics, especially those prepared from polymeric or resin materials, by providing coatings thereon to improve such properties.
It is a further object of this invention to provide a process for preparing foamed plastics having improved high temperature and flame resistance over the properties manifested by commercially available foamed plastics.